Coating an alloy substrate

ABSTRACT

Examples relating to coating an alloy substrate are described. For example, techniques for treating a surface of the alloy substrate for coating the alloy substrate with an exterior coat include providing an alloy substrate of a die-casted metal alloy, the alloy substrate having a surface with multiple pores, and applying an electrically conductive layer on the surface of the alloy substrate. The electrically conductive surface is composed of metal particles and electrically conductive polymers, and the electrically conductive layer is applied such that the metal particles fill the multiple pores on the surface of the alloy substrate. Thereafter, an oxidation process is performed on the surface to form an oxidation layer over the surface. The oxidation layer provides for adhesion of the surface with the exterior coat.

BACKGROUND

Metal alloys exhibit a wide variety of characteristics that make themsuitable for different applications ranging from commercial andindustrial materials to military and medical equipment. In general, thetype of properties possessed by a metal alloy is determined by theconstituents of the metal alloy. The properties possessed by a metalalloy, in turn determine use of the metal alloy for a given application.

The properties and characteristics of the metal alloys can be customizedduring manufacturing of the alloys, depending upon composition of thealloy, and process used for fabricating such alloys. The process ofmanufacturing metal alloys is generally a controlled process. Thecomposition of the alloy as well as the process parameters are monitoredto obtain a metal alloy having characteristics in accordance with an endapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is provided with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Thesame numbers are used throughout the drawings to reference like featuresand components.

FIG. 1 illustrates a sectional view of an die-casted metal alloy with anexterior coat deposition, in accordance with an implementation of thepresent subject matter;

FIG. 2 illustrates different stages of treating a surface of an alloysubstrate for depositing an exterior coat, according to animplementation of the present subject matter;

FIG. 3 illustrates an example method for treating a surface of an alloysubstrate, according to an implementation of the present subject matter;and

FIG. 4 illustrates an example method for depositing an exterior coat onan alloy substrate, according to an implementation of the presentsubject matter.

DETAILED DESCRIPTION

Generally, metal alloys, such as magnesium alloys, titanium alloys andaluminum alloys have high surface porosity with large number of poresand cavities on their surfaces. The pores and cavities make the surfaceuneven, hard and chemically unstable for coating with other materials.Such large number of pores and cavities may also provide reduced surfacecontact of an applied material with the surface of the metal alloys andprevent the applied material to have sufficient binding with thesurface.

Further, the surface of the metal alloys is also reactive and tend tooxidize with gases of the atmosphere to form an unstable oxide layer onthe surface. The unstable oxide layer reduces stability of the surfacefor adhering to an exterior coat, and makes the surface chemicallyresistant towards different materials.

Therefore, to overcome such issues, the surface of the metal alloys aregenerally subjected to multiple surface treatment processes, followed bydeposition of a putty and the exterior coat. However, the multiplesurface treatment processes make the overall process of treating thesurface and applying the exterior coat complex, time and resourceconsuming.

In accordance with an implementation of the present subject matter,techniques for efficiently treating the surfaces alloy substrates aredescribed. The techniques reduce porosity and reactivity of the surfacesof the metal alloys and make the surfaces stable for adhering toexterior coats.

In an example implementation of the present subject matter, an alloysubstrate of a die-casted metal alloy is received. As would beunderstood, the die-casted metal alloy is obtained through casting ormolding of molten metal alloy in a die or a mold, and then cooling andsolidifying are performed to obtain the alloy substrate. The surface ofthe alloy substrate is porous having multiple pores on the surface.Thereafter, an electrically conductive layer is deposited on the surfaceof the alloy substrate. The electrically conductive layer is depositedon the surface to cover the surface entirely. In an example, theelectrically conductive layer may be deposited through a sprayingtechnique or may be deposited manually. The electrically conductivelayer may be composed of metal particles and electrically conductivepolymers.

After depositing the electrically conductive layer, the surface issubjected to a machining process that may include scrubbing andpolishing of the surface. During machining, excess material ofelectrically conductive layer may be removed and the surface is madesmooth by allowing the metal particles to fill the pores, therebyreducing porosity of the surface. After the metal alloys are machineprocessed, the surface of the alloy substrate is oxidized based on anoxidation process to form an oxidation layer on the surface.

The oxidation layer so formed provides stability to the surface foradhering to exterior coats and insulates the surface from the outsideenvironment to prevent direct exposure of the surface to the environmentand reduce reactivity of the surface and corrosion. After the surface isoxidized, an exterior coat including at least one coating layer isdeposited on the surface of the alloy substrate. The exterior coat mayprovide a smooth and lustrous appearance to the alloy substrate.

Thus, the described techniques of depositing the electrically conductivelayer and performing the oxidation efficiently reduce porosity andreactivity of the surface and enhance binding of an applied exteriorcoat with the surface. Further, the techniques provide a time andresource efficient mechanism of treating the surface and making thesurface stable for coating.

The above described techniques are further described with reference toFIGS. 1 to 4. It should be noted that the description and figures merelyillustrate the principles of the present subject matter along withexamples described herein and, should not be construed as a limitationto the present subject matter. It is thus understood that variousarrangements may be devised that, although not explicitly described orshown herein, embody the principles of the present subject matter.Moreover, all statements herein reciting principles, aspects, andexamples of the present subject matter, as well as specific examplesthereof, are intended to encompass equivalents thereof.

FIG. 1 illustrates a sectional view of a die-casted metal alloy 100 withan exterior coat deposition, according to an implementation of thepresent subject matter. The die-casted metal alloy 100, possesses auniform surface devoid of pores and is obtained on subjecting an alloysubstrate 102 to a surface treatment process, as per techniquesdescribed in herein. The description of the surface treatment process isprovided in details with reference to subsequent figures.

Referring to FIG. 1, the alloy substrate 102 is composed of a metalalloy, for instance, a magnesium alloy, a titanium alloy, or an aluminumalloy. The alloy substrate 102 may be fabricated through techniques ofmanufacturing alloys, such as molding or die-casting of the metal alloyusing a die wherein a molten metal alloy is poured and then allowed tocool to take the shape of the die. During manufacturing of the alloysubstrate various imperfections, such as gas and air entrapments mayoccur that result in formation of pores and cavities on the surface ofthe alloy substrate 102.

The die-casted metal alloy 100 has an electrically conductive layer 104deposited over the alloy substrate 102. The electrically conductivelayer 104 is composed of single or multiple layers of metal particlesand electrically conductive polymers. In one example, the metalparticles include one of aluminum particles, magnesium particles, andtitanium particles and the electrically conductive polymers can be oneof polylactene, polyphenylenevinylene, polythienylenevinylene,polythiophene, poly-3-alkylthiopene, polypyrrole, polyaniline,polyphenylene, polyphenylene sulfide and polyfuran, andpoly-3,4-ethylenedioxythiopene polystyrene sulfonate (PEDOT). Theelectrically conductive layer 104 reduces porosity of the surface byallowing the metal particles of the electrically conductive layer 104 tofill the pores and cavities of the surface of the alloy substrate 102.

In an example implementation, the die-casted metal alloy 100 includes anoxidation layer 106. In an example, the oxidation layer 106 is a denseceramic protective layer that provides hardness and stability to thesurface for binding with exterior coats and insulates the surface fromthe outside environment, thereby reducing reactivity of the surface. Inan example, the oxidation layer 106 may be a magnesium oxide (MgO) layerwith a thickness of about 3-15 micro meter (μm).

Further, the die-casted metal alloy 100 includes an exterior coat 108disposed on the oxidation layer 106. The exterior coat 108 may have acoating layer, such as a paint coat having several paint layers coatedon the die-casted metal alloy 100 to provide a color and a texture tothe surface. In an example, the coating layer may be a metallic coatcomposed of metallic powders. Such metallic coats provide a metallicluster to the surface of the alloy substrate 102. Further, the exteriorcoat 108 makes the alloy substrate 102 water resistant, smooth, and softand imparts an anti-bacterial, anti-smudge and anti-fingerprintcharacteristics to the alloy substrate 102. The die-casted metal alloy100 with the exterior coat having such characteristics may be used forapplications in electronic devices, such as making back covers andhousings for laptops, notebooks, and smartphones.

The details of various stages of treating the surface of the die-castedmetal alloy 100 for deposition of the exterior coat 108 have beenexplained in conjunction with description of FIG. 2.

FIG. 2 illustrates various stages 200 of treating the surface of a metalalloy, implemented by various units, according to an exampleimplementation of the present subject matter. For sake of explanation,each stage of the surface treatment process and coat deposition has beendescribed with reference to an alloy substrate 202. A unit, in contextof the present description, can be an apparatus, a machine or acombination of apparatuses or machines for performing an operation at astage. At different stages, different units interact with the alloysubstrate 202 to add the different layers deposited over the surface ofthe alloy substrate 202 to create the die-casted metal alloy, such asthe above-described die-casted metal alloy 100.

In an example implementation, the alloy substrate 202 is obtained forsurface treatment and exterior coat deposition. The alloy substrate 202is then subjected to application of an electrically conductive layer 206by an applying unit 204. In an example, the applying unit 204 may be aspraying apparatus or multiple spraying apparatuses for sprayingelectrically conductive material on the surface of the alloy substrate202 to form the electrically conductive layer 206 on the alloy substrate202. In another example, the electrically conductive layer 206 may bedeposited manually. In manual deposition, an amount of fluidelectrically conductive material is poured on the alloy substrate 202 tocover the surface of the alloy substrate 202 and the conductive materialis spread over the surface using a spreading apparatus, such as aplastic knife. The electrically conductive layer 206 is alike theelectrically conductive layer 104 described earlier and is composed ofmetal particles and conductive polymers. In an example, the electricallyconductive layer 206 allows formation of a ceramic oxide layer over thesurface of the alloy substrate 202. The ceramic oxide layer is composedof the metal particles that are filled in the pores and cavities of thesurface of the alloy substrate 202.

The alloy substrate 202 with the electrically conductive layer 206 isthen subjected to a machining process implemented by a machining unit208. The machining unit 208 may include machining tools and a polishingequipment for removal of excess electrically conductive material fromthe surface and scrub or brush the remaining conductive material topolish the surface. In an example, polishing is performed by rotatingthe polishing equipment on the surface of the electrically conductivelayer 206. The polishing of the surface allows the metal particles ofthe electrically conductive layer 206 to fill the pores and cavities ofthe surface to smoothen the surface and reduce porosity of the alloysubstrate 202. After completing the process of machining, a machinedalloy substrate 210 is obtained.

In an example implementation, an oxidation process is performed on themachined alloy substrate 210 by an oxidation unit 212. In an example,the oxidation process may be a Micro Arc Oxidation (MAO) and theoxidation unit 212 may include electrodes, a container with anelectrolyte, and transducers for performing the MAO of the alloysubstrate 202, and form an oxidation layer 214 on the surface of themachined alloy substrate 210. In an example, the MAO may be performed ata voltage of about 150-550 Volts (V) at a temperature of about 10-45degree Celsius (° C.) for a duration of about 2-10 minutes.

Further, different chemicals may be used during the MAO, for instance,as electrolyte or for aqueous solutions used for oxidation. Thechemicals includes sodium silicate, metal phosphate, potassium fluoride,potassium hydroxide or sodium hydroxide, fluorozirconate, sodiumhexametaphosphate, sodium fluoride, ferric ammonium oxalate, phosphoricacid salt, graphite powder, silicon dioxide powder, aluminum oxidepowder, metal powder and polyethylene oxide alkylphenolic ether. Thechemicals may be used along with water with the composition of about0.05-15 percent (%) of the amount of water at a pH value of about 8-13.The MAO enhances adhesion of the surface of the alloy substrate 202 withexterior coats applied on the alloy substrate 202 and prevents surfacepeeling issues.

After performing the oxidation, an exterior coat 216 is applied on themachined alloy substrate 210 by a coating unit 218. For example, thecoating unit 218 may be a paint apparatus or a spraying apparatus forspraying exterior coat material on the alloy substrate 202. The exteriorcoat 216 may include at least one coating layer. The coating layer maybe a paint coat having a paint layer or several paint layers. In anexample, the paint layers may be of different colors and appearances. Inan example, the paint layers include a single layer of an Ultraviolet(UV) coat or a Polyurethane (PU) coat. In another example, the paintlayers include a base coat along with either the UV coat or the PU coat.

In another example implementation, the coating layer of the exteriorcoat 216 may include a metallic coat, such as a metallic UV coat or ametallic PU coat. The metallic coat is deposited over the surface toprovide a metallic lustre to the alloy substrate 102. In an example, themetallic UV coat is deposited at a temperature of about 50-55° C., with600-1000 Millijoules (mj) UV exposure for a duration of about 10-12minutes. The metallic UV coat is composed of pearl, metal powders, dyesand color pigments. In another example, the metallic UV coat may becomposed of resins, such as polyurethane, polycarbonate, urethaneacrylates, polyacrylate, polystyrene, polyetheretherketone,polyacryletheretherketone, polyesters, fluoropolymers, and a mixture ofthe resins. The thickness of the metallic UV coat is about 10-25 μm.

The metallic PU coat may be composed of polyurethane or urethaneacrylates. In an example, the thickness of the metallic PU coat is about5-20 μm. In an example implementation, the metallic PU coat may bedeposited in two layers, a base coat (not shown in the figure) and a topcoat (not shown in the figure). In an example, the base coat isdeposited at a temperature of about 80-150° C. for a duration of about20-40 minutes. The base coat may be composed of barium sulfate, talc,dyes, metal powders and color pigments. The base coat may also includebase coat resin, such as polyurethane and acrylic-polyurethane and maycontain aluminum particles for metallic luster. Thereafter, the top coatmay be deposited at a temperature of about 80-140° C. for about 20-40minutes.

In an example, the coating layer of the exterior coat 216 may include aprimer and a powder coat (not shown in the figure) deposited on theoxidation layer 214 prior to depositing the metallic UV coat. In anexample, the primer and the powder coat may be deposited to enhanceadhesion and durability of exterior coats on sharp edges of the surface.The primer may be composed of resin such as epoxy, acrylic-epoxyhybrids, acrylics, polyurethane and acrylic-polyurethane. Further, theprimer may also contain fillers from a group of carbon black, titaniumdioxide, clay, mica, talc, barium sulphate, calcium carbonate, syntheticpigments, metallic powders, aluminium oxide, CNT, graphene, graphite,organic and inorganic powders.

The powder coat is composed of high ratio fillers such as talc, clay,graphene and high aspect ratio pigments. Further, the powder coat mayinclude epoxy, poly (vinyl chloride), polyamides, polyesters,polyurethanes, acrylics, polyphenylene ether. The primer resin may besubjected to a temperature of about 80-160° C. for about 20-40 minutes.In an example, the powder coat and the primer may contain fillers fromcarbon black, titanium dioxide, clay, mica, talc, barium sulphate,calcium carbonate, synthetic pigments, metallic powders, aluminiumoxide, CNT, graphene, graphite, organic and inorganic powders.

After depositing the exterior coat 216 by the coating unit 218, adie-casted metal alloy 220 having the substrate alloy 202 with theexterior coat 216 as the top most layer is received. The describedtechniques provide for a surface treatment process including depositingan electrically conductive layer and an oxidation layer to reduceporosity and reactivity of the alloy substrate 102.

FIG. 3 and FIG. 4 illustrate methods 300 and 400 for treating surface ofan alloy substrate for deposition of exterior coats. The order in whichthe methods 300 and 400 is described is not intended to be construed asa limitation, and any number of the described method blocks may becombined in any order to implement the methods 300 and 400, or analternative method.

FIG. 3 illustrates the method 300 for treating surface of an alloysubstrate, according to an example implementation of the present subjectmatter. The surface of the alloy substrate generally has large number ofpores and cavities that makes the surface uneven and resistant forcoating with different materials. Further, the surface is also reactivewith gases of the atmosphere and is unstable for holding exterior coatsapplied on the surface. Therefore, to reduce porosity and reactivity ofthe surface and make the surface stable for adhesion with exteriorcoats, a surface treatment process is performed. The exterior coat maybe a single layer or multiple layers of paint material or a metalliccoat deposited on the alloy substrate for providing smooth and lustrousappearance to the alloy substrate.

At block 302, an electrically conductive layer is applied on the alloysubstrate. The electrically conductive layer is composed of metalparticles and electrically conductive polymers. The electricallyconductive layer is applied such that the metal particles fill themultiple pores on the surface of the alloy substrate.

Thereafter at block 304, the alloy substrate is subjected to anoxidation process to form an oxidation layer over the surface. Theoxidation layer provides for adhesion of the surface with an exteriorcoat. The alloy substrate 102 with the exterior coat is a die-castedmetal alloy, such as the above-described die-casted metal alloy 100 and220 with characteristics of a surface quality that may be used invarious applications, for example, making housing and back covers ofelectronic devices.

FIG. 4 illustrates the method 400 for treating surface of an alloysubstrate and deposit an exterior coat, according to another exampleimplementation of the present subject matter.

At block 402, an alloy substrate is received. The alloy substrate is adie-casted metal alloy and has a surface which is porous with multiplepores and cavities. As would be understood, the alloy substrate may beobtained after molding or die-casting of the metal alloy in a die or amold and the pores and the cavities may be due to imperfections, such asgas and air entrapment during molding or die-casting of the metal alloy.At block 404, an electrically conductive layer is deposited on thesurface of the alloy substrate. The electrically conductive layer iscomposed of metal particles and electrically conductive polymers.

In an example, the metal particles can be one of aluminum particles,magnesium particles, and titanium particles and the electricallyconductive polymers can be one of polylactene, polyphenylenevinylene,polythienylenevinylene, polythiophene, poly-3-alkylthiopene,polypyrrole, polyaniline, polyphenylene, polyphenylene sulfide andpolyfuran, and poly-3,4-ethylenedioxythiopene polystyrene sulfonate(PEDOT). In an example implementation, the electrically conductive layer104 may be deposited over the alloy substrate 102.

After depositing the electrically conductive layer, the surface of thealloy substrate is subjected to a machining process to smoothen thesurface by allowing the metal particles to fill pores of the alloysubstrate, at block 406. Therefore, the machining process reducesporosity of the surface of the alloy substrate 102. In an example, themachining process may include scrubbing, brushing or polishing of thesurface to remove excess electrically conductive material from thesurface of the alloy substrate.

Thereafter, at block 408, an oxidation process is performed onto thesurface to oxidize the surface and form an oxidation layer on thesurface. The oxidation layer provides stability to the alloy substrateto adhere to exterior coats and reduces reactivity of the alloysubstrate. The oxidation layer also provides hardness to the alloysubstrate. In an example implementation, the oxidation process is theMAO process and the oxidation layer 106 is formed over the surface ofthe alloy substrate 102.

At block 410, the exterior coat is deposited on the surface of the alloysubstrate. The exterior coat may include a single coating layer ormultiple coating layers. In an example, the exterior coat may be a paintcoat with a color and a smooth texture. The exterior coat may bedeposited to provide a lustrous appearance to the alloy substrate withanti-bacterial, anti-fingerprint, anti-smudge and water resistantcharacteristics.

In another example implementation, the exterior coat may be a metalliccoat composed of metallic powders, pearl, dyes, and color pigments. Inan example, the metallic coat may include a metallic Ultraviolet (UV)coat or a metallic PU (Polyurethane) coat. The metallic coat provides ametallic luster appearance to the alloy substrate 102. The alloysubstrate coated with the metallic coat may then be used for applicationin electronic devices as back cover for laptop, notebook andsmartphones.

The die-casted metal alloy obtained by the described method of surfacetreatment, may be used for various purposes where a metal alloy sheetwith non-porous surface having high adherence to exterior coating isdesired. For example, the die-casted metal alloy may be used tomanufacture back covers for electronic devices, such as laptops andsmart phones.

Therefore, the described techniques efficiently reduce porosity andreactivity of the metal alloys to enhance binding between an exteriorcoat and the surface of the metal alloys. Further, the describedtechniques provide a time and resource efficient mechanism of treatingthe surface of the metal alloys.

Although implementations of present subject matter have been describedin language specific to structural features and/or methods, it is to beunderstood that the present subject matter is not necessarily limited tothe specific features or methods described. Rather, the specificfeatures and methods are disclosed and explained in the context of a fewimplementations for the present subject matter.

What is claimed is:
 1. A method comprising: receiving an alloysubstrate, wherein the alloy substrate is a die-casted metal alloyhaving a surface which is porous; depositing an electrically conductivelayer on the surface of the alloy substrate, wherein the electricallyconductive layer is composed of metal particles and electricallyconductive polymers; subjecting the surface of the alloy substrate to amachining process to smoothen the surface by allowing the metalparticles to fill pores on the surface; performing an oxidation processonto the surface to oxidize the surface and form an oxidation layer overthe surface; and depositing an exterior coat on the alloy substrate, theexterior coat comprising at least one coating layer.
 2. The method asclaimed in claim 1, wherein the metal alloy includes at least one of amagnesium alloy, an aluminum alloy and a titanium alloy.
 3. The methodas claimed in claim 1, wherein the oxidation process is a Micro ArcOxidation (MAO).
 4. The method as claimed in claim 3, wherein the MAO isperformed at a voltage of about 150-550 Volts (V).
 5. The method asclaimed in claim 1, wherein thickness of the oxidation layer is about3-15 micro meter (μm).
 6. The method as claimed in claim 1, wherein theelectrically conductive polymers comprises at least one of polylactene,polyphenylenevinylene, polythienylenevinylene, polythiophene,poly-3-alkylthiopene, polypyrrole, polyaniline, polyphenylene,polyphenylene sulfide and polyfuran, and poly-3,4-ethylenedioxythiopenepolystyrene sulfonate (PEDOT).
 7. The method as claimed in claim 1,wherein the at least one coating layer includes a metallic coat, themetallic coat comprising a layer of at least one of metal powder, pearl,dyes and color pigments.
 8. The method as claimed in claim 7, whereinthe metallic coat comprises one of a metallic Ultraviolet (UV) coat anda metallic Polyurethane (PU) coat.
 9. A method comprising: applying, ona surface of a alloy substrate, an electrically conductive layer, theelectrically conductive layer composed of metal particles andelectrically conductive polymers, wherein the metal particles fillmultiple pores on the surface of the alloy substrate; and subjecting thealloy substrate to an oxidation process to form an oxidation layer overthe surface, wherein the oxidation layer provides for adhesion of thesurface with an exterior coat.
 10. The method as claimed in claim 9,wherein the oxidation process is a Micro Arc Oxidation (MAO).
 11. Themethod as claimed in claim 9 further comprising applying the exteriorcoat on the alloy substrate, wherein the exterior coat comprises atleast one coating layer, the coating layer comprising at least one of apaint layer and a metallic coat.
 12. A die-casted metal alloycomprising: an alloy substrate, wherein surface of the alloy substrateis porous; an electrically conductive layer on the alloy substrate, theelectrically conductive layer comprising metal particles andelectrically conductive polymers, wherein the metal particles are filledin pores of the surface of the alloy substrate to smoothen the surface;an oxidation layer on the electrically conductive layer, the oxidationlayer being formed based on an oxidation process; and an exterior coaton the oxidation layer, the exterior coat composed of at least onecoating layer.
 13. The die-casted metal alloy as claimed in claim 12,wherein the at least one coating layer includes a metallic coat, themetallic coat comprising one of a metallic Ultraviolet (UV) coat and ametallic Polyurethane (PU) coat.
 14. The die-casted metal alloy asclaimed in claim 13, wherein thickness of the metallic coat is about10-25 micrometer (μm).
 15. The die-casted metal alloy as claimed inclaim 12, wherein the at least one coating layer includes a base coat,the base coat comprising at least one of barium sulfate, talc, dyes,metal powders and color pigments.